> At http://www.firebirdsql.org/en/downloads the available release of
> Firebird to download is 2.5.2.

2.5.2 Update 1 is the latest official/production-ready release.

> Somebody mentioned a 2.5.3 release. Is there a 2.5.3 release? I exist,
> where can I download it?

Only as a snapshot build.
http://www.firebirdsql.org/en/snapshot-builds/



--
With regards,
Thomas Steinmaurer
http://www.upscene.com/

Professional Tools and Services for Firebird
FB TraceManager, IB LogManager, Database Health Check, Tuning etc.